This section is separated from that on leprosy in clothing Leviticus 13:47-59 with which it would seem to be naturally connected, and is placed last of all the laws concerning leprosy, probably on account of its being wholly prospective. While the Israelites were in the wilderness, the materials of their dwellings were of nearly the same nature as those of their clothing, and would be liable to the same sort of decay. They were therefore included under the same law.
I put the plague - Yahweh here speaks as the Lord of all created things, determining their decay and destruction as well as their production. Compare Isaiah 45:6-7; Jonah 4:7; Matthew 21:20.

And the Lord spake unto Moses and unto Aaron,.... At the same time as the above laws were delivered concerning the leper, and the cleansing of him, or however immediately upon that; the affair of the leprosy of houses being what belonged to the priest to examine into and cleanse from:
saying; as follows.

The leprosy in a house is unaccountable to us, as well as the leprosy in a garment; but now sin, where that reigns in a house, is a plague there, as it is in a heart. Masters of families should be aware, and afraid of the first appearance of sin in their families, and put it away, whatever it is. If the leprosy is got into the house, the infected part must be taken out. If it remain in the house, the whole must be pulled down. The owner had better be without a dwelling, than live in one that was infected. The leprosy of sin ruins families and churches. Thus sin is so interwoven with the human body, that it must be taken down by death.

The law concerning the leprosy of houses was made known to Moses and Aaron, as intended for the time when Israel should have taken possession of Canaan and dwell in houses. As it was Jehovah who gave His people the land for a possession, so "putting the plague of leprosy in a house of the land of their possession" is also ascribed to Him (Leviticus 14:34), inasmuch as He held it over them, to remind the inhabitants of the house that they owed not only their bodies but also their dwelling-places to the Lord, and that they were to sanctify these to Him. By this expression, "I put," the view which Knobel still regards as probable, viz., that the house-leprosy was only the transmission of human leprosy to the walls of the houses, is completely overthrown; not to mention the fact, that throughout the whole description there is not the slightest hint of any such transmission, but the inhabitants, on the contrary, are spoken of as clean, i.e., free from leprosy, and only those who went into the house, or slept in the house after it had been shut up as suspicious, are pronounced unclean (Leviticus 14:46, Leviticus 14:47), though even they are not said to have been affected with leprosy. The only thing that can be gathered from the signs mentioned in Leviticus 14:37 is, that the house-leprosy was an evil which calls to mind "the vegetable formations and braid-like structures that are found on mouldering walls and decaying walls, and which eat into them so as to produce a slight depression in the surface."
(Note: Cf. Sommer (p. 220), who says, "The crust of many of these lichens is so marvellously thin, that they simply appear as coloured spots, for the most part circular, which gradually spread in a concentric form, and can be rubbed off like dust. Some species have a striking resemblance to eruptions upon the skin. There is one genus called spiloma (spots); and another very numerous genus bears the name of lepraria.")